1. Field of the Invention
The present invention generally relates to hearing aids and to methods of controlling hearing aids. More specifically, the invention relates to hearing aids with a directional capability, based on reception of sound in at least two microphones. Still more specifically, the invention relates to noise reduction, and, particularly, to the reduction of the noise received by a hearing aid user, through a hearing aid being of the type with multiple microphones. The invention still more particularly relates to a system for controlling the directional characteristic of sound input systems.
2. The Prior Art
Hearing aids having a directional sound receiving characteristic are useful to improve speech perception in noisy environments, where sound signals may be received simultaneously from different directions, as is the case e.g. in the noise environment frequently referred to as cocktail party noise. With a directional sound receiving characteristic, e.g. in the shape of a cardioid or super cardioid characteristic, the perception ot speech received in a hearing aid from directions in front of the user may be improved by reducing the reception of sound coming from the back of the user, while maintaining the level of sound coming from the area in front of the user. On the other hand, in environments with only a low noise level or no significant speech signals the hearing aid user will normally prefer an omnidirectional or spherical sound receiving characteristic, offering the same perception of sound irrespective of the direction, from which it arrives.
U.S. Pat. No. 5,757,933 shows a directional controller employing two microphones and a switch. The switch allows the user to switch between a directional mode and a omnidirectional mode. The function of the directional controller is to provide the user with a possibility of reducing the sound receiving characteristic of the microphone system for undesired signals that are spatially separated from a desired signal.
U.S. Pat. No. 5,259,033 shows a parameter controller with an LMS-algorithm.
U.S. Pat. No. 5,757,933 shows a directional controller employing two microphones and a switch. The switch allows the user to switch between a directional mode and a omnidirectional mode. The function of the directional controller is to provide the user with a possibility of reducing the sound receiving characteristic of the microphone system for undesired signals that are spatially separated from a desired signal.
U.S. Pat. No. 5,259,033 shows a parameter controller with an LMS-algorithm.
U.S. application Ser. No. 09/445,485, filed Dec. 7, 2000, now abandoned, provides a hearing aid with a controllable directional characteristic, which may change from an omnidirectional to a directional characteristic and vice versa. The hearing aid has two spaced apart microphones and a directional controller including a delay device for delaying the signal from one of the microphones. The hearing aid may be changed between a directional mode and an omnidirectional mode. The delay may be adjusted in order that the direction of the canceling effect is controlled.
U.S. application Ser. No. 09/696,264, filed Oct. 26, 2000, as a c-i-p of U.S. application Ser. No. 09/445,485 mentioned above, provides a method for controlling the directionality of the sound receiving characteristic of a hearing aid comprising spaced apart microphones, wherein the sound receiving characteristic may change between an omnidirectional characteristic and a directional characteristic. In this hearing aid, an adjustable time or phase delay may be imposed. The directional characteristic may be created by adjusting the delay of the delay device to be the same as the acoustical delay between the back microphone and the front microphone. With this delay, the signals, that are first received at the back microphone and are later received at the front microphone, are suppressed in the adding circuit, where the delayed signal of the back microphone is subtracted from the output signal of the front microphone. The hearing aid may exercise a smooth change-over between an omnidirectional characteristic and a directional characteristic, substantially without changing the phase relationship or time delay and the amplitude characteristic of the signals.
Such a directional control provides the user with the possibility of altering the sound receptive property of the hearing aid, whereby it is possible to reduce the influence of a noise source on the users perception of a desired sound source. However, it would be an advantage if the hearing aid it-self would be able to control the directional characteristic.